This invention relates in general to surgical needles and, more particularly, to improvements in a biopsy needle and a biopsy needle stylet which optimize cutting and withdrawal of tissue specimens during a biopsy procedure.
A biopsy needle of the character to which the present invention relates is a side cut needle such as that disclosed in U.S. Pat. No. 3,477,423 to Griffith. Such a side cut needle includes a solid stylet telescopically received within an inner tubular cutting cannula which in turn is telescopically received within an outer tubular cannula in which the stylet and inner cannula are supported for axial and rotative displacement relative to one another and to the outer cannula. The stylet is provided with a specimen cutting recess, or tissue receptacle, in the distal portion thereof by which a tissue specimen severed at the biopsy site is removable therefrom. More particularly, the side cut needle is inserted into a patient until the distal end of the outer cannula reaches the lesion where the biopsy specimen is to be taken, and the stylet is then advanced relative to the outer and inner cannulas into the lesion to the biopsy site. The tissue at the site moves into the specimen recess, and the inner cannula is then advanced relative to the outer cannula and over the stylet to cut the tissue into the specimen recess and to cover the recess and thus entrap the specimen therein for removal from the site. Such removal is achieved by retracting the stylet and inner cutting cannula into the outer cannula and then withdrawing the needle from the patient.
Heretofore, the cutting recess in the stylet component of a biopsy needle has been defined by an axially extending bottom wall parallel to the axis of the stylet and axially spaced apart end walls perpendicular to the bottom wall and thus the stylet axis. When the stylet is advanced into the area from which tissue is to be removed, the tissue enters the recess as the stylet advances therethrough and the tissue is severed and captured in the recess by advancement of the inner cutting cannula relative to the stylet. With a recess of the foregoing structure, it is difficult to obtain a desirable quantity of specimen tissue in the cutting recess and, in this respect, it is not uncommon to withdraw a specimen which, from the standpoint of quantity, is only one-half to three-quarters the quantity which would be removed if the cutting recess were completely filled. This deficiency is due at least in part to the difficulty in maintaining stability with respect to the position of the stylet at the biopsy site during advancement of the cutting cannula relative thereto. When the component parts of the biopsy needle are manually manipulated, for example, there is a tendency to advance and/or withdraw the stylet from its initial position at the biopsy site during advancement of the cutting cannula. Both of these movements cause a portion of the specimen initially received in the cutting recess to be displaced therefrom whereby, when severing is completed by advancement of the cutting cannula, the quantity of tissue captured in the recess is less than that which is possible based on the size of the recess. As another example, biopsy needles of the foregoing structure are often operated through the use of a "gun" by which displacement of the component parts of the needle is automated during the biopsy procedure, and there is a recoil action in connection with such automated guns which tends to push the stylet forwardly from its initial position at the biopsy site during advancement of the cutting cannula. As mentioned above, such advancement of the stylet further into the tissue at the biopsy site causes a portion of the tissue in the cutting recess to be displaced therefrom.
It is believed that the tissue loss encountered with a stylet structured and operated as referred to above is the result of the perpendicular disposition of the end walls of the recess relative to the bottom wall thereof. In this respect, as the stylet is advanced or withdrawn relative to the tissue site during advancement of the cutting cannula, the end walls at the opposite ends of the recess move against the tissue specimen and the perpendicular disposition of the walls tends to deflect the tissue laterally outwardly of the recess. Thus, the quantity of tissue which is captured in the recess upon completing the advancement of the cutting cannula is reduced relative to the optimum capability of the recess.